There has been a technique that decolorizes colors of an image by applying heat to a sheet on which the image has been formed with toners whose colors are erased at a prescribed temperature or higher. As a device that is used in this image decolorization, a decolorizing device of a roll heating type, which erases an image on a sheet by passing the sheet between a roller pair including a heating roller and a pressure roller in pressure contact with the heating roller, has been generally employed.
In heating of a sheet surface in the roll heating technique, a lamp as a heat source is included in the heating roller formed of a metal pipe. The pipe surface is warmed from the inner surface of the heating roller by radiant heat that is generated from the lamp.
However, in the configuration, since the entire pipe is warmed, a long heating time is required until the heating roller surface reaches a set temperature. In addition, as another problem, since the entire pipe is uniformly heated, even if there is an area that may not be decolorized, the same energy is applied, causing unnecessary power consumption.